Phytases catalyze the hydrolysis of phytate (myo-inositol hexakisphostate), a major storage form of phosphorus in plant seeds (Reddy et al., “Phytates in Legumes and Cereals,” Adv. Food Res. 28:1-92 (1982)), to phosphate and myo-inositol, and render phytate-phosphorus bio-available to animals. Therefore, phytases have been used as an animal feed supplement to improve the bioavailability of phytate phosphorus and other minerals to simple-stomached animals, such as swine and poultry (Gentile et al., “Effectiveness of an Experimental Consensus Phytase in Improving Dietary Phytate-phosphorus Utilization by Weanling Pigs,” J. Anim. Sci. 81:2751-7 (2003); Lei et al., “Supplemental Microbial Phytase Improves Bioavailability of Dietary Zinc to Weanling Pigs,” J. Nutr. 123:1117-23 (1993); Casey & Walsh, “Identification and Characterization of a Phytase of Potential Commercial Interest,” J. Biotechnol. 110:313-22 (2004); Lei & Porres, “Phytase Enzymology, Applications, and Biotechnology,” Biotechnol. Lett. 25:1787-94 (2003)). However, none of the natural phytases, including the commercially available phytases, can meet the requirements for industrial use (Lei & Stahl, “Biotechnological Development of Effective Phytases for Mineral Nutrition and Environmental Protection,” Appl. Microbiol. Biotechnol. 57:474-81 (2001)). The temperature during the processing of feed pelleting can reach as high as 70-90° C. (Mullaney et al., “Advances in Phytase Research,” Adv. Appl. Microbiol. 47:157-99 (2000)). Phytases with sufficiently high thermal stability to withstand these higher temperatures are desirable, but rare among the naturally-occurring sources of phytase (Lei & Stahl, “Biotechnological Development of Effective Phytases for Mineral Nutrition and Environmental Protection,” Appl. Microbiol. Biotechnol. 57:474-81 (2001)). As an ideal phytase will need to function well in the digestive tract of animals, the enzyme should also be effective at a pH ranging from 2.5 to 3.5 (Konietzny & Greiner, “Molecular and Catalytic Properties of Phytate-degrading Enzymes (Phytases),” Int. J. Food Sci. Tech. 37(7):791-812 (2002)).
Thus, there remains a need for improved phytases with greater thermostability and pH profile. The present invention is directed to overcoming these and other deficiencies in the art.